Vs a piloted aircraft? The difference is there but not in the realm of 2:1. As more tech gets loaded on them I suspect they'll reach parity with manned systems. The issue isn't so much wartime cost but the fleet cost as a whole. You get X drones from your budget and they cost a lot of money to maintain (not dissimilar to manned aircraft) so you can't always just have enough to make up for time in transit.

Even so, what if China responds with their own drones and takes advantage of their higher sortie rates?

^there we go. I forgot to mention this. Sortie rates favor the defender if the attacker is far enough away. If A and B have 10 planes each and A's planes take 1 hour to kill something but B's planes take 2, A will win even with a significant technological disadvantage because you have to kill half their fleet before you reach parity.